I 
THE COLOURS OF ORGANISMS 
15 
the sculpturing of butterflies’ scales has been extolled 
by most possessors of a microscope, while savage 
and civilised races are alike in their admiration for 
the feathers of birds. The fact that organisms so 
widely separated as are birds and butterflies are 
alike in exhibiting both exquisite structural colora¬ 
tion and a wonderful development of structures 
arising from the cuticle, suggests that the structural 
colours are in origin merely a result of extreme 
differentiation of the cuticle, and therefore produced 
by the same cause which gave rise to this differentia¬ 
tion. The presence of brilliant iridescence in some 
of the mud-inhabiting worms is therefore not quite 
inexplicable, for here also we find that the cuticle 
shows a considerable amount of differentiation. We 
can also further understand how it is that the highest 
pitch of perfection is attained in birds and butterflies, 
when we consider that in both cases the colouring 
occurs in connection with structures which are of 
supreme importance to the species, that is, with the 
feathers of the bird and the scales, which are but 
outgrowths of the wings, in butterflies. 
Production of Light by Organisms (Phos¬ 
phorescence), its Distribution and Meaning 
The production of light, the phenomenon commonly 
though incorrectly spoken of as phosphorescence, is 
so striking a characteristic of many organisms that 
it deserves notice here in our consideration of colours. 
It is unnecessary to enter into a detailed account of 
the theories of Dr. Carpenter and others as to the 
probable use of this characteristic, because these 
